\begin{tabular}{l*{5}{l}}
\toprule
                    &\multicolumn{5}{c}{}                                            \\
                    &$\bar{z}_{n}^{(1)}$&$\bar{z}_{n}^{(2)}$&$\text{Nunn}^{\text{con}}_{n}$&$\text{Nunn}^{\text{lib}}_{n}$&$\text{Levchenko}_{n}$\\
\midrule
$\bar{z}_{n}^{(1)}$&        1.00&            &            &            &            \\
$\bar{z}_{n}^{(2)}$&        0.96&        1.00&            &            &            \\
$\text{Nunn}^{\text{con}}_{n}$&        0.37&        0.34&        1.00&            &            \\
$\text{Nunn}^{\text{lib}}_{n}$&        0.38&        0.36&        0.99&        1.00&            \\
$\text{Levchenko}_{n}$&        0.32&        0.37&        0.68&        0.61&        1.00\\
\bottomrule
\end{tabular}
